Epidemiological surveys of genetic diseases or neoplasms and detailed studies of families at high risk of cancer may help detect environmental and genetic influences in carcinogenesis. In addition, identification of families prone to malignancy has therapeutic implications, enabling surveillance and early diagnosis of neoplasms. Review of prior medical and environmental history; documentation of history; collection and distribution of biological specimens; review of hospital records of series of patients with selected genetic diseases or neoplasms; and survey of childhood cancer death certificates in the U.S. since 1960. A number of families have been studied with site-specific tumors and many of the tumors which occur together in familial syndromes also exist in studies of multiple primary cancer, suggesting a familial cancer syndrome may represent a "scattering" over the family tree of tumors which share etiologic influences. Results of laboratory specimens of various cancer families are being obtained and assembled. Studies of families at high risk of cancer may help to detect environmental and genetic influences in carcinogenesis. The same approach will be continued, using new laboratory methods and epidemiologic clues from other sources as necessary.